Open AccessPhylogenomics Reveals a Diverse Rickettsiales Type IV Secretion System
Author(s) -
Joseph J. Gillespie,
Kelly A. Brayton,
Kelly P. Williams,
Marco A. Quevedo Diaz,
Wendy C. Brown,
Abdu F. Azad,
Bruno Sobral
Publication year - 2010
Publication title -
infection and immunity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.508
H-Index - 220
eISSN - 1070-6313
pISSN - 0019-9567
DOI - 10.1128/iai.01384-09
Subject(s) - biology , rickettsiales , genome , genetics , bacterial genome size , horizontal gene transfer , gene , secretion , computational biology , biochemistry
With an obligate intracellular lifestyle,Alphaproteobacteria of the orderRickettsiales have inextricably coevolved with their various eukaryotic hosts, resulting in small, reductive genomes and strict dependency on host resources. Unsurprisingly, large portions ofRickettsiales genomes encode proteins involved in transport and secretion. One particular transporter that has garnered recent attention from researchers is the type IV secretion system (T4SS). Homologous to the well-studied archetypalvir T4SS ofAgrobacterium tumefaciens , theR ickettsiales v ir h omolog (rvh ) T4SS is characterized primarily by duplication of several of its genes and scattered genomic distribution of all components in several conserved islets. Phylogeny estimation suggests a single event of ancestral acquirement of thervh T4SS, likely from a nonalphaproteobacterial origin. Bioinformatics analysis of over 30Rickettsiales genome sequences illustrates a conserved corervh scaffold (lacking only avirB5 homolog), with lineage-specific diversification of several components (rvhB1 ,rvhB2 , andrvhB9b ), likely a result of modifications to cell envelope structure. This coevolution of thervh T4SS and cell envelope morphology is probably driven by adaptations to various host cells, identifying the transporter as an important target for vaccine development. Despite the genetic intractability ofRickettsiales , recent advancements have been made in the characterization of several components of thervh T4SS, as well as its putative regulators and substrates. While current data favor a role in effector translocation, functions in DNA uptake and release and/or conjugation cannot at present be ruled out, especially considering that a mechanism for plasmid transfer inRickettsia spp. has yet to be proposed.